1. Field
Embodiments of the present invention generally relate to data storage systems, and more particularly, to write heads for thermally assisted recording.
2. Description of the Related Art
Higher storage bit densities in magnetic media used in disk drives have reduced the size (volume) of magnetic bits to the point where the magnetic bit dimensions are limited by the grain size of the magnetic material. Although grain size can be reduced further, the data stored within the cells may not be thermally stable. That is, random thermal fluctuations at ambient temperatures may be sufficient to erase data. This state is described as the superparamagnetic limit, which determines the maximum theoretical storage density for a given magnetic media. This limit may be raised by increasing the coercivity of the magnetic media or by lowering the operational temperature of magnetic hard drive. Lowering the temperature may not always be practical when designing hard disk drives for commercial and consumer use. Raising the coercivity, on the other hand, will make it challenging for current write heads to do the recording.
One additional solution has been proposed, which uses magnetic media with high coercivity without the need to increase the magnetic moment of write pole material. The solution heats up a localized area on the media to a temperature above Curie temperature, thereby, lowering the effective coercivity of the localized region and thus, enabling writing with current write heads within this heated region. The data state becomes “fixed” once the media cools below Curie temperature. This technique is broadly referred to as “thermally assisted (magnetic) recording” (TAR or TAMR), “energy assisted magnetic recording” (EAMR), or “heat-assisted magnetic recording” (HAMR) which are used interchangeably herein. It can be applied to longitudinal and perpendicular recording systems as well as “bit patterned media”. Heating of the media surface has been accomplished by a number of techniques such as focused laser beams or near-field optical sources.
While the laser beam or the near-field optical source is positioned to induce heating in the magnetic media, a certain percentage of heat will also be generated in the magnetic head. This heating can affect the shape of the head at the media facing surface, such as an air bearing surface (ABS), and therefore impact the fly height. Heating of the head can also impact the reliability and performance of the head because high temperatures can accelerate thermal migration of various films and structures, causing inter-diffusion and dimensional changes.
The primary areas of the HAMR head that get hot are the near-field transducer (NFT) and magnetic pole placed proximate to the NFT. The antenna material is comprised of noble metals with low melting point and hence can show morphological changes at moderate temperatures in the range of 150 to 400 degrees Celsius. Therefore, there is a need in the art for an improved recording head for HAMR.